I run a very small Raspbian installation off a 1GB SD card. I discovered devtmpfs uses 20% of all space.

Output of df -h:

Filesystem      Size  Used Avail Use% Mounted on
rootfs          788M  690M   97M  88% /
/dev/root       788M  690M   97M  88% /
devtmpfs        212M     0  212M   0% /dev
tmpfs            44M  184K   44M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            88M     0   88M   0% /run/shm
/dev/mmcblk0p1   50M   19M   32M  37% /boot

What is devtmpfs and how can I reduce its size?

  • Maybe you want to take a look to your output of "top"... devtmpfs just uses the amount of mem it needs for the moment not the amount of mem shown from output of "df". So maybe most of all everything is fine with this.
    – user28419
    Mar 27, 2015 at 10:56
  • 1
    Not directly answering the question, but it is worth mentioning that the size of tmpfs (and its variant devtmpfs) is just a highwater-mark. It marks how large the filesystem can grow, not how much RAM it takes. tmpfs only takes the RAM for the files actually written to it.
    – smokku
    May 14, 2022 at 16:14

2 Answers 2


tmpfs indicates a TeMPorary FileSystem. So the devtmpfs has partitioned off 212M of your RAM and not your SD Card.

devtmpfs is the mountpoint name for the /dev directory /dev is the location of special or device files. http://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/dev.html

Reducing the size may have consequences I'm not aware of so proceed with caution. To reduce it, modify /etc/mtab and adjust the size= part of the devtmpfs entry

  • 5
    No, please NEVER ever edit /etc/mtab. That is generated based on /etc/fstab and keeps track of currently mounted filesystems. See <pre>man mount</pre>
    – der_do
    Mar 9, 2015 at 18:35
  • 1
    Note that for tmpfs the size is a maximum size. It is not using 212mb, it's using (next to) 0mb. Thats because device files are nothing more than a name and a reference, there's no file data. So the only memory overhead is holding the file names / permissions etc in memory. Jun 22, 2017 at 12:40

The size for tmpfs is set in

You can use percentage-of-total-ram values there.

Please note, that providing too little space for /tmp might lead to unexpected results.

Resizing devtmpfs can be done in /etc/init.d/udev (around line 116). There is a variable


  • 1
    I have no such thing in /etc/init.d/udev on my Raspbian 7.6. Mar 9, 2015 at 19:26

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